In some of conventional vehicle engines, a camshaft and other accessories are driven by power transmitted from a crankshaft. In a power transmitting structure of these engines, an axial end of the crankshaft protrudes from a cylinder block and is fixed to a sprocket or pulley. A driven member such as camshaft is also fixed to a sprocket or pulley. Both of the sprockets or pulleys are engaged with a chain or a belt. In addition, the chain or belt is covered by a cover member (chain cover member or belt cover member, hereinafter chain cover member) fixed to an engine end in an axial direction of the crankshaft.
However, the chain cover member resonates with vibrations of the crankshaft and also transmits outside noises generated by the chain (or belt), and thus it is desired to reduce such noises transmitted from the chain cover member. In order to overcome this problem, there has been developed a chain cover member having a number of polygonal concave surfaces or convex surfaces formed on its surface to reduce vibrations (for example, see Japanese Patent No. 3412759).
Although the configuration of the chain cover member described above achieved the reduction of vibrations, it is likely to generate sound emission through resonance due to flat portions remaining in the concaves or convex surfaces. Therefore, it is desired to reduce sound emission from the cover member more significantly.